Telephone system



Sept. 12, 1939. R. TAYLOR ET AL 2,172,947

TELEPHONE SYSTEM Filed Jan. 29 1936 5 SheetsSheet 1 .Llllilllll.

I! III I p -12,1939. RQTAYLQR Em 2,112 941 TELEPHONE SYSTEM FiledJan. 29, 1936 5 Sheets-Sheet 2 Sept. 12, 1939. R. TAYLOR ET AL" 2,172,947

TELEPHONE SYSTEM I Filed Jan. 29, 1956 5 Sheets-Sheet 3 flaw/4m 73 no? Gaza: 72/04/45 544 5? Sept. 12, 1939. R. TAYLOR ET AL TELEPHONE SYSTEM Filed Jan. 29, 1936 5 Sheets-Sheet 4 Sept. 12, 1939. R. TAYLOR ET AL TELEPHONE SYSTEM Filed Jan. 29, 1936 5 Sheets-Sheet 5 K m2 1 ma a Mano A. Q. Z uf w. fm 6 2 .b a JVI Q Z 4 r m w 5 .H s w 5 no t A 8 V E III D. 00 L Q0 T T l Patented Sept. 12, 1939 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application January 29, 1936, Serial No. 61,289 In Great Britain February 6, 1935 6 Claims.

The present invention relates to improvements in automatic or semi-automatic telephone systems and the particular object of the invention is to provide an improved arrangement for insuring efiicient use of the bank contacts of the switches employed in such systems. The invention has particular application in connection with final selector switches whether serving P. B. X. groups of lines or single lines or both, although it is not limited thereto, and by its assistance the establishment and the distribution of the lines in P. B. X. groups is greatly facilitated. For example, if it is required to extend a P. B. X. group, adjacent sets of spare contacts are not now essential and it is possible by means of the invention to group together spare contacts in indiscriminate positions and associate them with any desired P. B. X. group of lines.

According to one of the features of the invention if the selector switch encounters a busy condition a signal is transmitted to apparatus common to a number of said switches and the further control of the switch including its resetting on to a different line leading in the same direction or the transmission of a busy signal if no such line is available is effected by the common apparatus. By this means the changes in existing final selectors are reduced to a minimum.

According to a further feature of the invention on a busy line or busy group of lines being encountered means are provided adapted to respond to such busy condition to effect the release and resetting of the switch on to an idle line having access to the same subscriber connected in another part of the switch bank or to give a busy signal if there is no such line available.

According to another feature of the invention, in order to enable the switch to be reset in the event of the line or group of lines first tested be-' ing found busy a switch having access to a'number of different groups of final selector switches is adapted to be taken into use such switch having associated therewith, means for indicating the particular line or group of lines being tested, means for ascertaining if there is an idle line leading to the required subscriber and means for controlling the resetting of the final selector switch onto such idle line if no idle line is available causing a busy signal to be given.

According to yet another feature of the invention, in order to enable the switch to be reset in the event of the line or group of lines first tested being found busy, apparatus common to a plurality of final selectors is adapted to be associated therewith said apparatus comprising means for determining the level on which the switch is resting, means for causing the switch to advance step by step to a predetermined position on the level so as to determine the contact on the level, means for ascertaining if there is an idle line leading to the required subscriber and means for causing the switch to be reset on to such idle line.

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawings comprising Figs. l6 of which Fig. 1 is a trunking diagram, while Figs. 2-5 when assembled as shown in Fig. 6 show the circuit connections.

Referring now to the trunking diagram, FS represents a final selector to which the facilities of group extension are provided. GP represents common group pilot apparatus which conveniently may be provided in duplicate for one hundred final selectors such as FS. With the group pilot apparatus GP there is associated a finder switch F, a marking switch M, both adapted to move in ,two directions, and one or more auxiliary line selecting switches ALH adapted to move in a single direction, and an impulse control switch S.

The operation is briefly as follows:

When the final selector FS encounters a busy 1 condition on any line whatever a start circuit is completed to the common group pilot apparatus GP. This causes the finder F to hunt to find the final selector in question. When this is done the marker switch M begins to operate, firstly to the level on which the final selector FS is resting and secondly the rotary magnets of the two switches will step in unison until wipers of the final selector FS have reached a particular positionsay the eleventh, when the movement of both switches ceases and the marker switch M rests on contacts corresponding to the contacts on which the final selector hasencountered the busy condition. If this contact has no auxiliary lines associated with it the group pilot apparatus is at once released and the final selector is caused to send a busy tone to the calling subscriber. If however, the contact in question is one of a P. B. X. group which has auxiliary lines, the final selector is at once released and astart circuit is extended to the auxiliary line selecting switch ALI-I which hunts first of all to find the first line ini the auxiliary group associated with the line or P. B. X. group selected and if that line is busy and is not the only line in the auxiliary group it will hunt to find an idle line in the auxiliary group. On finding a free line, the line is immediately busied. The final selector is then directively set as regards its vertical and rotary movements by the impulse sending switch S, which in turn is controlled in accordance with the particular line selected by the switch ALH. The switching relay in the final selector is then operated to switch through to the selected line and the group pilot apparatus is restored for further use.

It will be understood that the invention may be applied to existing types of final selector switches, whether those having acccess to individual lines only or to P. B. X. groups of lines only or to both individual lines and P. B. groups of lines, as well as being incorporated in the design of new circuits.

Referring now to the operation of the circuit, it should be explained that only the elements of a typical P. B. X. final selector necessary for the understanding of the invention are shown and these will be found to the left of the vertical dotted line in Figs. 2 and 4. With the exception of the busy condition the operation of the P. B. X. final selector takes place in the usual manner and the circuit modifications necessary for adapting the busy condition to start up the group pilot apparatus will be fully appreciated from the description which follows.

When a P. B. X. final selector encounters a busy condition its relay G operates and at contacts gl or 92 connects resistance battery respectively to the odd or even level start con ductor OLS or ELS leading to the group pilot apparatus, and at the same time at contact 93 or 94 extends a marking battery to the vertical bank AWFof the finder to indicate the level in which the final selector is located. The dotted connection shunting contact g3 applies only to the 0 level. The provision of odd and even level start conductors leading to the main and duplicate group pilot apparatus respectively evens up the load on the equipment and enables one to act as an auxiliary to the other in the event of a fault. The connection of resistance battery to the odd level start conductor causes relay SA to operate in series with relay SB which is marginal and only operates when two or more final selectors located on odd finder levels encounter a busy condition simultaneously. In this case the function of relay SB is to extend the start circuit to the duplicate group pilot apparatus so that both finders are taken into use and the waiting time is reduced. Relay SA at armature sal operates the start relay ST Fig. 5 which in turn at armature stl Fig. 4 completes a self-interrupted driving circuit to the vertical magnet VF of the finder. The finder accordingly steps its wipers in search of the marked level and when this is found a circuit is completed over the vertical bank AWF for operating relay LK over both its windings in series. Relay LK thereupon at armature lkl disconnects the driving circuit to the vertical magnet and completes a locking circuit for LK over its left hand winding which is sufiiciently low in resistance to mark the level selected as busy to the other finders. At armature 21% the following self interrupted driving circuit is completed to the rotary magnet RF of the finder switch: earth at the interrupter springs cm Fig. 2, wiper SI and first bank contact of the sender switch, interrupter springs rm, of the marker switch, armature rs3, interrupter springs 17 of the finder, oiT normal springs NM! of the marker, armature 003, off normal springs NF! of the finder,

armature Z702 to the rotary magnet RF. The wipers Fl to F8 of the finder are therefore rotated in search of the final selector in question and when this is found earth from the G relay circuit is picked up by wiper F8 of the finder and causes the comparatively high resistance relay RS to operate in series with magnet RF. The resistance YF in parallel with relay RS is of a comparatively low value and serves to check the operation of the magnet. The metal rectifier MRB prevents earth from the magnet circuit feeding back to relay RS and wiper F8. Relays RS in operating at armature rsl disconnects the resistance YF, at armatures rs2 and T33 extends potential through relay VT and the wiper F"! of the finder to mark the vertical bank AWP of the final selector, at armature r54 extends a corresponding marking to the vertical bank AWM of the marker switch, at armature 7'85, Fig. 2 connects the high resistance relay HR to wiper F2 of the finder so that it operates in series with the switching relay of the final selector which is not energised at this time, and finally at armature Ts! Fig. 2 completes a self-interrupted driving circuit to the vertical magnet VM of the marker switch which thereupon commences to hunt vertically. It should, be explained here that the vertical bank AWM of the marker switch, Fig. 4, is multiplied with the vertical banks AWP of all final selectors served by the group pilot in question so that it will be understood that the marking potential applied to relay VT is extended over the vertical bank of the final selector to mark a particular level in the vertical bank of the marker switch corresponding to the level on which the Wipers of the final selector are resting. Accordingly when the wipers of the marker switch are raised to the marked level, relay VT operates and at armature vtl, Fig. 2, opens the driving circuit to the magnet VM and removes a short circuit from the high resistance relay VTR which thereupon operates in series with the magnet, the latter however not energising in this circuit. Since the marker switches of both group pilots may be hunting at the same time on simultaneous calls, it is important to ensure that the respective relays VT shall be operated only from their own marking switches and to this end the vertical wiper or marker switch No. 1 is connected to earth and the vertical wiper of marker No. 2 is connected to battery as indicated by the alternative connections shown in the drawings. Furthermore, as VT relays are each connected to the centre point of a potentiometer resistance it is necessary to include metal rectifiers MBA in their circuit connected up in opposite senses so that there shall be no danger of a marker switch stopping on a level marked via the finder associated with the other marker switch.

There is also the possibility of both VT relays being connected together due to the finders of both group pilots being set to corresponding levels. In these circumstances the rectifiers are obviously without effect but as both VT relays present the same potential, no current flows and consequently no false operation results.

Relay HR in operating at armature hrl completes a local holding circuit for relay ST, Fig. 5, atarmaturehrZ disconnects relays SA and SB and at armature m3 provides a local holding circuit for relay RS. Returning to the operation of relay VTR, at armature vtrl a further point is opened in the short circuit path about its winding, at armature vtrZ, Fig. 4, the rotary magnet RM of the marker is energised and at armature vtrd earth is connected to wiper F6 of the finder to energise the rotary magnet IRM of the final selector. When the rotary magnet RM fully energises the interrupter springs rm open and disconnect the short circuiting earth from one side of the winding of relay GA, and further when the rotary magnet IRM of the final selector fully operates the associated sprinys 7" close and connect earth to the wiper and bank F5 of the finder to operate relay GA over one winding in series with resistances YA and YB. Relay GA thereupon at armature gaZ and ga3 opens the circuits to both rotary magnets which accordingly release. Interaction therefore takes place between the final selector and marker rotary magnets and relay GA so that when the wipers of the final selector come into their 11th position the wipers of the marker switch will have been moved to a complementary position corresponding to the busy contact in question.

In the l lth position cam springs S in the final selector operate and connect earth over bank and wiper F4 of the finder to hold relay GA in series with relay EC which also operates. Relay GA in holding prevents further interaction between the rotary magnets while relay EC' at armature ecZ and 603 connects relays EL and CO respectively to the Wiper F! of the finder. It should be explained here that all contacts in the bank Fl of the finder corresponding to final selectors serving the same hundred group of lines are commoned together and connected .to a particular wiper of the marker switch as indicated in the drawings and it will be obvious therefore that, while wiper Fl of the finder selects the correct 108 line group, the wiper of the marker switch selects the contact in that hundred line group which has been selected and found busy by the final selector.

If the contact in question has no auxiliary lines associated with, it is jumpered direct to earth which is extended over the wiper of the marker switch and the wiper of the finder to operate relay CO. Relay C0 looks over its armature col, and at armature 002 short circuits the high resistance winding of relay HR to bring about the switching of relay-H in the final selector. The operation of relay H with the wipers in the llth position causes busy tone to be extended to the calling subscriber and relay HR is short circuited and released by the locking armature of relay H. Relay HR in turn releases relays ST and RS at armatures hr] and m3 respectively. On the release of armature r53 2. self-interrupted driving circuit is completed to the rotary magnet RM of the marker switch which accordingly rotates its wipers to the end of the bank and restores to normal whereupon the circuit is opened at the off normal springs NMI and transferred to the rotary magnet RF of the finder. The finder therefore in turn rotates its wipers to the end of the bank and restores to normal and the circuit is opened at off normal springs NFI. During the homing operations of the respective switches in the group pilot apparatus a circuit is completed over off normal springs NM2 or NFZ and the resting armature st5 for operating relay RG, Fig. 5, which provides a guarded release condition by opening the operating circuit to relays SA and SB and temporarily transferring the start circuit to the other group' pilot apparatus. Should the switch fail to restore within a reasonable period the continued connection of battery over armature m2, Fig. 5, to the common conductor [3 causes a release alarm to be actuated.

If the line in question has auxiliary lines associated with it, the contact in the marker switch bank will be jumpered to a contact in the bank ALI-I4 of the auxiliary line hunter corresponding to the first of the auxiliary group of lines. As the wiper of the marker switch fails to pick up earth under these conditions a short circuit is not presented to the high resistance relay EL,

Fig. 2, which therefore operates in series with relay CO: which remains normal. Relay EL thereupon locks by way of its armature e13 in series with the vertical magnet VM of the marker switch, at armature e22 extends earth over the wiperFl in the finder and the marker switch wiper selected to mark the first contact of the auxiliary group of lines in the bank ALH4, and atarmature ell extends earth over the low resistance Winding of relay EC to wiper F6 of the finder to energise the rotary magnet of the final selector. The final selector therefore steps to its 12th position from which it releases to normal. Relay EL at armature e14, Fig. 3, completes a self-interrupted driving circuit to the magnet ALM of the auxiliary line hunter ALH which thereupon rotates its wipers in search of the position marked by the marker switch and corresponding to the first line of the auxiliary group. associated with the busy line in question.

When this is found relay IG operates when the interrupter springs alm open and at armature lg5 temporarily disconnects the driving magnet ALM and at armature lgl prepares a circuit for the upper winding of relay [H in series with the lower winding of relay lG to the wiper and bank ALH3 which connects with the private normals of the auxiliary lines. If the first line is busy wiper ALH3 will encounter earth so that relay IH does not operate and when the interrupter springs alm again close relay l G is short circuited and released and the switch ALH takes a further step. This action takes place automatically until a free line is found and it will be uderstood that the group of contacts in the bank ALI-I4 corresponding to the auxiliary group of lines are connected together and earthed over the marking circuit in order that relay IG may be operated to prepare the test circuit to relay III at each step of the switch ALH.

When a free line is found relay IH operates from battery supplied by the subscribers cut-off relay and looks over its lower winding and the make-first armature Ihl, and at armature lh2 the upper high resistance winding of relay lH is short circuited and relay IG now holds over its lower low resistance Winding in series with the cut off relay in the called subscribers line circuit. The line selected is thus guarded and relay lG at armature I holds open the driving circuit to the magnet and at armature I94 connects earth to the wipers and banks ALH5 and ALHG to make two markings in the bank S3 of the sender switch, as determined by the jumpering shown in the drawing, to control the generation of a train of impulses necessary directively to set the final selector into engagement with the auxiliary line found by the switch ALH. Relay IH therefore at armature Ih3 extends earth from the sender switch magnet springs sm to the finder wiper F4 to energise the vertical magnet of the final selector which accordingly raises the wipers one stepand at the conclusion of the magnet stroke the springs 12 close and connect earth over the bank and wiper F5 of the finder to energise the sender switch driving magnet SM. The magnet SM therefore prepares for the advancement of the wipers SI to S3 on to the next set of contacts and at the conclusion of the magnet stroke opens the springs sm thereby de-energising the vertical magnet of the final selector. This action continues automatically until the final selector is raised to the desired level, whereupon wiper S3 of the sender switch encounters the first earthed marking and upon the opening of springs sm relay SS operates in series with the vertical magnet. Relay SS looks over its armatures sat and at armature ss3 operates relay SZ which also locks and in turn at armatures $22 and 8.23 transfers the driving circuit from the vertical magnet IVM to the rotary magnet ERM of the final selector and at the same time short circuits and releases relay SS. When armature 882 restores to normal the rotary magnet of the final selector now interacts with the driving magnet of the sender switch and when the final selector wipers have been set to the desired contact wiper S3 of the sender switch encounters the second earthed marking. On the opening of the springs sm relay CO now operates in series with the rotary magnet of the final selector and brings about the operation of the H relay to switch the final selector on to tht auxiliary line. The final selector now takes over the call and performs its functions in the usual manner while the release of relay HR, following the energisation of the H relay of the final selector initiates the release of the group pilot apparatus which restores for further use.

If the auxiliary line hunter fails to find an idle line, relay BC is operated from wiper and bank ALI-I2 at the commencement of the second revolution, and at armature D03 and 1904 makes the position I and i l in the bank of the sender switch S. Relay BC also at armature bcZ operates relay H which looks and causes the sender switch to interact with the final selector as described so that the wipers of the latter are set to the 11th position on the first level. The final selector therefore, transmits busy tone to the calling subscriber in the manner previously described and the group pilot apparatus is released for further use.

In case the final selectors are arranged to serve 280 line groups, relay WS in the group pilot apparatus is operated, under the appropriate conditions, from earth extended over the wiper and bank F3 from the final selector and at armatures wsi to 1.084 changes over the connections to the wipers of the marker switch in order to establish connection with the correct hundred line group.

The delayed alarm relays TA and RG, Fig. 5, are provided for the purpose of supervising the operation of the group pilot apparatus and in case it fails to fulfil its function within a predetermined period of time an alarm is provided and the group pilot in question is switched out of service.

As regards the operation of these relays, it will be remembered that relay ST is operated immediately the group pilot is taken into use and accordingly at its armature st3 connects relay TA to the common conductor extending to the motor driven cam S. The Z cam is also driven on the same shaft as the S cam and the function of these cams is to deliver earth pulses alternately to the common conductors shown at, conveniently, 6 second intervals.

Upon the application of the S pulse relay TA operates and locks over its other winding, at armature ta2 prepares relay RG for the reception of the vZ pulse and at armature we prepares the circuit to conductor Ill extending to the supervisory alarm apparatus. If the group pilot apparatus fails to complete its function within the period allowed relay TA remains operated and upon reception of the Z pulse relay RG is operated and locked in series with relay ST. Relay RG at armature m2 connects resistance battery to conductor It] to operate the supervisory alarm apparatus, at armatures rg3 and rgd connects earth to the common conductors H and I2 to operate rack and main exchange alarms, at armature r95 routes further calls intended for this group pilot to the other group pilot, at armature r96 opens the busy marking to the vertical bank, at armature 1g! opens the circuit to the vertical magnet of the finder and at armature 1'g3 Fig. lights the supervisory lamp LP individual to the group pilot apparatus under fault. The exchange attendant is thus notified of the fault condition and by tracing back the various alarms the faulty group pilot is quickly located and the fault attended to.

It should be understood that while the actual final selector circuit referred to is that proposed for use with switches which step on release to the 12th position on a level and then fall in the vertical direction, the invention is also applicable to final selectors of other constructions in which the release takes place by a backward movement along the path over which the wipers were set. Further the invention is not necessarily limited to switches having movement in two directions as it can be equally applied to switches having movement in a single direction. It is also possible by suitable circuit re-arrangement for the 11th step contacts in the various levels to be utilised for auxiliary lines and in these circumstances it will be arranged that the busy circuit is rendered ineffective when the switch is directively set to the 11th position.

We claim:

1. In a telephone system, a final selector switch, a group of lines accessible to said switch, means effective if said switch is set on the first line of said group and said line is found busy for releasing said switch, means for testing the lines of said group to find an idle line, and means for directively reoperating said switch to connect with such idle line.

2. In a telephone system, a plurality of groups of final selectors, each group having access to groups of lines, common means effective whenever any final selector is operated to select a group of lines and finds the first line of he group busy for identifying the operated final selector and the selected group of lines, means for releasing the final selector, means for finding an idle line in the selected group, and means for directively reoperating the final selector to con nect with such idle line.

3. In a telephone system, a final selector switch, groups of lines accessible to said switch, means effective if said switch is operated to select a group of lines and finds the first line busy for releasing said switch, means for testing the lines of the selected group to find an idle line, and a sender controlled by said testing means for transmitting impulses to said switch to reoperate it to connect with the idle line.

4:. In a telephone system, a plurality of final selectors, groups of lines accessible to said selectors, a finder having access to said selectors, means responsive to a selector being operated to select a group and finding the first line of the group busy for operating the said finder to connect with the operated selector, a marker and means for operating it to identify the selected group, a testing switch controlled by said marker to find an idle line in the selected group, means for releasing the operated selector, and a sender controlled by said testing switch to transmit impulses through the finder to the selector after it is released to reoperate it to connect with the idle line.

5. In a telephone system, a connector switch, a group of lines accessible to said switch, said switch being directively operable to connect with the first line of said group whenever it is idle, means responsive whenever the first line of said group is busy when said switch is directively operated thereto for determining the busy line on which said switch is resting and for restoring said switch to normal, means for finding an idle line in said group of lines and for making such line busy, and means for automatically resetting said switch to connect with the line busied by said last mentioned means.

6. In a telephone system, a connector switch,

'a group of lines accessible to said switch, said switch being directively operable to connect with the first line of said group whenever it is idle, an auxiliary switch operable to find said connector whenever the first line of said group is busy when said connector switch is directively operated thereto, a marker switch, means controlled by said auxiliary switch for operating said marker switch to find the busy line, a line selecting switch, means controlled by said marker switch for controlling said line selecting switch to find an idle line in said group of lines and for restoring said connector switch to normal, and means controlled by said line selecting switch reoperating said connector switch to connect with the line found by said line selecting switch.

REGINALD TAYLOR. GEORGE THOMAS BAKE-R. 

